1. Field of the Disclosure
This disclosure relates to a liquid crystal display device, and particularly to a liquid crystal display device including an alignment layer of thermal stability, and a manufacturing method thereof.
2. Description of the Related Art
Nowadays, liquid crystal display (LCD) devices have been highlighted as one of next-generation high-tech display devices, because of their features such as less consumption power, superior portability, techno-intensiveness, high added value and so on. The LCD device includes a liquid crystal panel for displaying an image depending on the light transmittance, and a backlight for providing light to the liquid crystal panel. The liquid crystal panel includes a lower substrate having a TFT (Thin Film Transistor) and a pixel electrode, an upper substrate having a black matrix and a color filter and arranged to face the lower substrate, and a liquid crystal layer interposed between the two substrates.
The characteristics of the liquid crystal panel, for example, light transmissivity, viewing angle, and contrast, are closely related to the alignment characteristic of liquid crystal. Accordingly, to align liquid crystal in a particular direction on the liquid crystal panel, an alignment layer is formed on a substrate before the liquid crystal is formed. To form the alignment layer, a rubbing process, in which a rubbing cloth makes physical contact with the substrate on which an alignment material is formed, is widely used. The rubbing process may generate static electricity that can damage the TFT formed on the substrate and contaminate the surface of the alignment layer.
To solve the problem in the rubbing process, a liquid crystal alignment method in a non-contact manner has been researched. The non-contact type method may be a light irradiation method that includes a photoisomerization method, a photodegradation method, and a photopolymerization method.
Of the methods, the photodegradation method is to align liquid crystal by generating optical anisotropy using a photodegradation reaction, that is, a partial combination of molecules is selectively cut in a particular direction by irradiating light to an organic substance including a light alignment material. In the photodegradation method, since the molecular weight of the organic substance included in the alignment layer decreases as the alignment layer is formed while the organic substance is decomposed itself, the thermal characteristic of the alignment layer may be deteriorated. Accordingly, when thermal stress is applied to the alignment layer, the alignment force of the alignment layer is deteriorated so that the alignment of the liquid crystal may be deformed. As a result, it is more control the liquid crystal alignment and a residual image, that is, brightness of a particular area of the alignment layer to which the thermal stress is applied may abnormally increase.